Explosive fracturing of geological formations surrounding oil and gas wells and geothermal wells is often required to release the oil and gas from the formation or to yield an adequate flow of heated fluid from a geothermal formation. Numerous single component, liquid explosives for explosive fracturing of oil or gas formations are known. Examples of single component explosives are desensitized nitroglycerine, diethylene glycol dinitrate/dinitrotoluene/trinitrotoluene, nitromethane combined with varying amounts of sensitizing additives, and nitrobenzene or nitrotoluene combined with sensitizing additives. Some of the nitromethane based explosives depend upon the addition of glass microballoons to operate reliably at the high hydrostatic pressures commonly encountered at the bottom of deep, fluid-filled wells. All these single component explosives have the common disadvantage of requiring large quantities of explosives to be stored on the earth's surface at the wellhead near operating personnel, constituting an unnecessary potential hazard. For example, if premature detonation should initiate downhole from an unforeseen cause, the detonation would propagate up through the tubing employed to transfer the explosive downhole and could cause a disastrous explosion at the wellhead, which could be injurious to both personnel and property.
The disadvantages of a single component, liquid explosive can be avoided by separating the explosive formulation into two nondetonable components. The two components, in liquid, molten or slurried form, can then be separately fed downhole and mixed at a safe distance below ground level. The two components can be mixed at the desired explosion situs, or can be mixed in a downhole mixer and then pumped to the section of the well where the geological formation is to be fractured. Then, if a premature downhole detonation should occur, the detonation cannot propagate any farther than the below ground location where the components are mixed, insuring the safety of personnel and property at the wellhead.
Well stimulation methods employing two component explosives are known. Fuel and oxidizer components for such two component explosives are also known. However, such known components are not suitable for high temperature downhole environments such as those encountered in geopressured or geothermal reservoirs. Such two component explosives are insufficiently thermally stable to be of practical value, because one or both of the components degrade at high temperatures, reducing or eliminating the explosive power of the explosive. Additionally, these prior art explosives are subject to premature detonation at the high temperatures encountered in many geological formations.
An additional problem associated with some prior art explosives is their relatively large failure diameter, which eliminates the possibility of detonating the explosive through sand filled regions commonly encountered in geothermal formations. Prior art explosives known to have a small failure diameter are incapable of withstanding the high temperatures found in geothermal wells.
Accordingly, it is a broad object of the present invention to provide two nondetonable, liquid or low melting components that can be easily mixed in liquid form at a remote location to form an explosive composition. It is a further object of the present invention to provide such a two component explosive that has the capability of withstanding high temperature environments for periods of at least 6 hours, and preferably for periods of at least 24 hours. It is a further object to provide such a two component explosive that can withstand temperatures on the order of 475.degree. K. for at least 24 hours and can withstand temperatures of up to 560.degree. K. for shorter periods without premature detonation or deflagration, and without significant loss of explosive power.
Further objects of the present invention are to provide such a two component explosive that is noncorrosive, nontoxic and environmentally acceptable; to provide such a two component explosive that has low mechanical shock, friction, electrostatic discharge and adiabatic compression sensitivity; to provide such a two component explosive that has a high detonation velocity and a small failure diameter; and to provide components for such an explosive that are readily available at a relatively low cost, that can be pumped downhole or otherwise transferred downhole and mixed downhole, and that are soluble in water to facilitate clean-up of equipment.
It is a further object of this invention to provide a nondetonable, solid, mixed composition that can be safely handled aboveground and that, upon lowering into the geothermal well and melting, becomes detonable when initiated by a cap, by a cap with booster, or by a cap with a shaped charge.